Back to EveryPatent.com
| United States Patent |
5,719,705
|
|
Machol
|
February 17, 1998
|
Anti-static anti-reflection coating
Abstract
An anti-reflection coating that is soil resistant and easy to maintain is
provided. The coating includes a multilayer film having alternating layers
of high and low refractive index materials that comprise electrically
conductive metal oxides. The film is formed by reacting metal with
non-stoichiometric amounts of oxygen such that the coating has one or more
layers of electrically conductive metal oxide material. The coating is
particularly suited for ophthalmic applications.
| Inventors:
|
Machol; Steven N. (Sebastopol, CA)
|
| Assignee:
|
Sola International, Inc. (Menlo Park, CA)
|
| Appl. No.:
|
487365 |
| Filed:
|
June 7, 1995 |
| Current U.S. Class: |
359/581; 359/582; 359/585; 427/164 |
| Intern'l Class: |
G02B 001/10 |
| Field of Search: |
359/581,582,585,507
351/62
427/164
|
References Cited
U.S. Patent Documents
| 3708225 | Jan., 1973 | Misch et al. | 351/160.
|
| 3962488 | Jun., 1976 | Gillery | 427/109.
|
| 4611892 | Sep., 1986 | Kawashima et al. | 359/581.
|
| 4957358 | Sep., 1990 | Terada et al. | 359/512.
|
| 5181141 | Jan., 1993 | Sato et al. | 359/581.
|
| 5190807 | Mar., 1993 | Kimock et al. | 428/216.
|
| 5362552 | Nov., 1994 | Austin | 359/588.
|
| 5372874 | Dec., 1994 | Dickey et al. | 428/216.
|
| 5508135 | Apr., 1996 | Lelental et al. | 430/63.
|
| 5536580 | Jul., 1996 | Ikadai et al. | 359/586.
|
| 5541770 | Jul., 1996 | Pellicori et al. | 359/585.
|
| 5582919 | Dec., 1996 | Ikadai et al. | 359/585.
|
| Foreign Patent Documents |
| 0203730 | Dec., 1986 | EP | 359/581.
|
| 53-28214 | Aug., 1978 | JP | .
|
| A 62-244001 | Oct., 1987 | JP | 359/581.
|
Primary Examiner: Dzierzynski; Paul M.
Assistant Examiner: Juba, Jr.; John
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis, L.L.P.
Claims
What is claimed is:
1. A method of fabricating a high transmittance ophthalmic lens which
comprises the steps of:
providing a transparent ophthalmic lens; and
forming, on a surface of said ophthalmic lens, a transparent, electrically
conductive and substantially static resistant anti-reflection coating by
reacting a metal with an effective non-stoichiometric amount of oxygen
such that the coating comprises at least one layer of electrically
conductive metal oxide material.
2. The method of claim 1 wherein the coating of the ophthalmic lens in the
neutral state has an electric potential that is less than about 100 volts.
3. The method of claim 2 wherein the coating surface has an electric
potential that is less than about 600 volts when measured immediately
after being rubbed with a cloth.
4. The method of claim 3 wherein the coating surface has an electric
potential that is less than about 100 volts within about 5 seconds of
being rubbed by the cloth.
5. The method of claim 4 wherein the ophthalmic lens does not include a
hydrophobic outer layer over the anti-reflection coating.
6. The method of claim 1 wherein said coating is formed by electron beam
ion-assisted deposition.
7. A method of fabricating a high transmittance ophthalmic lens which
comprises the steps of:
providing a transparent ophthalmic lens; and
forming, on a surface of said ophthalmic lens, a transparent, multilayer,
substantially static resistant, anti-reflection coating wherein at least
one layer is electrically conductive by reacting a metal with an effective
non-stoichiometric amount of oxygen such that the coating comprises at
least one layer of electrically conductive metal oxide material.
8. The method of claim 7 wherein each of the at least one electrically
conductive layer is formed by electron beam evaporation whereby metal
reacts with non-stoichiometric amounts of oxygen to form an electrically
conductive metal oxide.
9. The method of claim 7 wherein each of the at least one electrically
conductive layer is a high refractive index material that comprises
niobium oxides.
10. The method of claim 7 wherein each of the at least one electrically
conductive layer is a high refractive index material that comprises
titanium oxides.
11. The method of claim 7 wherein the multilayer anti-reflection coating
comprises alternating high and low refractive index materials such that
each layer has a refractive index different from that of any adjoining
layer, wherein the index of refraction of each low refractive index
material is less than about 1.5 at a wavelength of about 550 nm, wherein
the index of refraction of each high refractive index material is greater
than about 2.0 at a wavelength of about 550 nm, and wherein at least one
layer comprises an electrically conductive metal oxide material.
12. The method of claim 11 wherein the high refractive index material
comprises titanium oxides and wherein the low refractive index material
comprises silicon oxides.
13. The method of claim 11 wherein the high refractive index material
comprises niobium oxides and wherein the low refractive index material
comprises silicon oxides.
14. The method of claim 11 wherein the multilayer anti-reflection coating
comprises:
(i) a first layer having an index of refraction from about 2.0 to about
2.55 and that is about 7 to about 15 nm thick;
(ii) a second layer having an index of refraction from about 1.38 to about
1.5 and that is about 15 to about 40 nm thick;
(iii) a third layer having an index of refraction from about 2.0 to about
2.55 and that is about 90 to about 130 nm thick; and
(iv) a fourth layer having an index of refraction from about 1.38 to about
1.5 and that is about 55 to about 105 nm thick, wherein the indices of
refraction are measured at a reference wavelength of 550 nm.
15. The method of claim 14 wherein the third layer is electrically
conductive.
16. The method of claim 11 further comprising the step of depositing an
adhesion layer onto the ophthalmic lens surface prior to forming said
multilayer anti-reflection coating thereon.
17. The method of claim 7 wherein the at least one electrically conductive
layer is formed by reactive sputtering whereby metal reacts with
non-stoichiometric amounts of oxygen.
18. The method of claim 7 wherein the coating has a thickness of about 200
to about 500 nm.
19. The method of claim 7 wherein the at least one conductive layer is
formed by ion-assisted deposition.
20. The method of claim 7 wherein the at least one conductive layer is
formed by electron beam ion-assisted deposition.
21. The method of claim 7 wherein the at least one conductive layer is
formed by reactive sputtering.
22. A high transmittance ophthalmic lens comprising:
an ophthalmic lens substrate; and
a transparent, substantially static resistant multilayer film comprising
alternating layers of high refractive index and low refractive index
materials, wherein at least one layer of the multilayer film is
electrically conductive wherein the multilayer film comprises alternating
high and low refractive index materials such that each layer has a
refractive index different from that of any adjoining layer, wherein the
index of refraction of each low refractive index material is less than
about 1.5 at a wavelength of about 550 nm, wherein the index of refraction
of each high refractive index material is greater than about 2.0 at a
wavelength of about 550 nm, and wherein said at least one electrically
conductive layer comprise non-stoichiometric metal oxides.
23. The ophthalmic lens of claim 22 wherein the high refractive index
material comprises niobium oxides.
24. The ophthalmic lens of claim 22 wherein the high refractive index
material comprises titanium oxides.
25. The ophthalmic lens of claim 22 wherein the high refractive index
material comprises titanium oxides and wherein the low refractive index
material comprises silicon oxides.
26. The ophthalmic lens of claim 22 wherein the high refractive index
material comprises niobium oxides and wherein the low refractive index
material comprises silicon oxides.
27. The ophthalmic lens of claim 22 further comprises an adhesion layer
interposed between the substrate and the multilayer film.
28. The ophthalmic lens of claim 22 wherein the multilayer film comprises:
(i) a first layer having an index of refraction from about 2.0 to about
2.55 and that is about 7 to about 15 nm thick;
(ii) a second layer having an index of refraction from about 1.38 to about
1.5 and that is about 15 to about 40 nm thick;
(iii) a third layer having an index of refraction from about 2.0 to about
2.55 and that is about 90 to about 130 nm thick; and
(iv) a fourth layer having an index of refraction from about 1.38 to about
1.5 and that is about 55 to about 105 nm thick, wherein the indices of
refraction are measured at a reference wavelength of 550 nm.
29. The ophthalmic lens of claim 28 wherein the third layer is electrically
conductive.
30. The ophthalmic lens of claim 28 further comprises an adhesion layer
situated between the substrate surface and the multilayer film.
31. The ophthalmic lens of claim 28 wherein the multilayer film of the
ophthalmic lens in the neutral state has an electric potential that is
less than about 100 volts.
32. The ophthalmic lens of claim 31 wherein the multilayer film surface has
an electric potential that is less than about 600 volts when measured
immediately after being rubbed with a cloth.
33. The ophthalmic lens of claim 32 wherein the multilayer film surface has
an electric potential that is less than about 100 volts within about 5
seconds of being rubbed by the cloth.
34. The ophthalmic lens of claim 33 wherein the ophthalmic lens does not
include a hydrophobic outer layer over the multilayer film.
35. An ophthalmic lens fabricated by a process that comprises the steps of:
providing a transparent ophthalmic lens substrate; and
depositing, onto a surface of said substrate, a transparent, substantially
static resistant multilayer anti-reflection coating wherein at least one
layer is electrically conductive wherein the step of depositing said
coating comprises reacting metal with an effective non-stoichiometric
amount of oxygen to form a layer of electrically conductive metal oxide.
36. The lens of claim 35 wherein the layer of electrically conductive metal
oxide is formed by electron beam evaporation.
37. The lens of claim 35 wherein the layer of electrically conductive metal
oxide is formed by reactive sputtering.
38. The lens of claim 35 wherein the layer of electrically conductive metal
oxide layer is formed by ion-assisted deposition.
39. The lens of claim 35 wherein the layer of electrically conductive metal
oxide layer is formed by electron beam ion-assisted deposition.
40. An ophthalmic lens fabricated by a process that comprises the steps of:
providing a transparent ophthalmic lens substrate; and
depositing, onto a surface of said substrate, a transparent, substantially
anti-static multilayer film comprising alternating layers of high
refractive index and low refractive index materials wherein at least one
layer is electrically conductive wherein the multilayer film comprises:
alternating high and low refractive index materials such that each layer
has a refractive index different from that of any adjoining layer, wherein
the index of refraction of each low refractive index material is less than
about 1.5 at a wavelength of about 550 nm, wherein the index of refraction
of each high refractive index material is greater than about 2.0 at a
wavelength of about 550 nm.
41. The ophthalmic lens of claim 40 wherein the multilayer film of the
ophthalmic lens in the neutral state has an electric potential that is
less than about 100 volts.
42. The lens of claim 40 wherein the high refractive index material
comprises titanium oxides and wherein the low refractive index material
comprises silicon oxides.
43. The lens of claim 40 wherein the high refractive index material
comprises niobium oxides and wherein the low refractive index material
comprises silicon oxides.
44. The lens of claim 40 wherein the multilayer film comprises:
(i) a first layer having an index of refraction from about 2.0 to about
2.55 and that is about 7 to about 15 nm thick;
(ii) a second layer having an index of refraction from about 1.38 to about
1.5 and that is about 15 to about 40 nm thick;
(iii) a third layer having an index of refraction from about 2.0 to about
2.55 and that is about 90 to about 130 nm thick; and
(iv) a fourth layer having an index of refraction from about 1.38 to about
1.5 and that is about 55 to about 105 nm thick, wherein the indices of
refraction are measured at a reference wavelength of 550 nm.
45. The lens of claim 44 wherein the third layer is electrically
conductive.
46. The lens of claim 44 further comprising an adhesion layer situated
between the substrate surface and the multilayer film.
47. The lens of claim 46 wherein the coating is formed by electron beam ion
evaporation.
Description
FIELD OF THE INVENTION
The present invention relates to anti-reflection coatings for transparent
substrates such as ophthalmic lens and particularly to a method of
fabricating anti-reflection coatings that are anti-static and easy to
clean.
BACKGROUND OF THE INVENTION
Ophthalmic lenses have traditionally been formed as a single integral body
of glass or plastic. Recently, lenses have been fabricated by laminating
two lens wafers together with transparent adhesive. Regardless of how it
is constructed, an ophthalmic lens can include an anti-reflection coating
to improve transmittance of visible light.
Conventional anti-reflection coatings comprise multilayer structures
described for instance, in U.S. Pat. Nos. 3,432,225 and 3,565,509.
Conventional anti-reflection coatings have a hydrophobic outer layer,
which typically comprises a fluoroalkylchlorosilane, to promote soil
resistance and facilitate cleaning. Despite the presence of this outer
layer, ophthalmic lens surfaces nevertheless tend to attract airborne
particles. Furthermore, oil contaminants on the lens surface tend to
smudge rather than wipe off cleanly, making the lenses difficult to
maintain.
SUMMARY OF THE INVENTION
The present invention is directed to transparent articles such as
ophthalmic lens that are coated with an anti-reflection coating with
inherent anti-static properties. In addition to not attracting dust and
other air-borne contaminants, the durable inventive anti-reflection
coating is also easy to clean. Anti-reflection coatings of the present
invention do not require a hydrophobic outer layer.
Accordingly, one aspect of the invention is directed to a method of
fabricating a high transmittance article which comprises the steps of:
providing a transparent substrate; and forming, on a surface of said
substrate, a transparent, electrically conductive anti-reflection coating.
Another aspect of the invention is directed to a method of fabricating a
high transmittance article which comprises the steps of:
providing a transparent substrate; and
forming, on a surface of said substrate, a transparent multilayer
anti-reflection coating wherein at least one layer comprises an
electrically conductive high refractive index material or an electrically
conductive low refractive index material.
A feature of the invention is that the coating can be formed by reacting
metal with oxygen such that the coating comprises one or more layers of
electrically conductive metal oxide material. Techniques for accomplishing
this include electron beam reactive evaporation, ion-assisted deposition,
and reactive sputtering of metal targets.
In yet another aspect, the invention is directed to a high transmittance
article comprising:
a transparent substrate; and
a transparent multilayer film comprising alternating layers of electrically
conductive high refractive index and electrically conductive low
refractive index materials.
In a further aspect, the invention is directed to a substantially static
resistant ophthalmic lens fabricated by a process that comprises the steps
of:
providing a transparent substrate; and
depositing, onto a surface of said substrate, a transparent multilayer
anti-reflection coating wherein each layer comprises an electrically
conductive high refractive index or an electrically conductive low
refractive index material.
In another aspect, the invention is directed to a substantially anti-static
ophthalmic lens fabricated by a process that comprises the steps of:
providing a transparent substrate; and
depositing, onto a surface of said substrate, a transparent multilayer film
comprising alternating layers of high refractive index and low refractive
index materials wherein each layer is electrically conductive.
In a preferred embodiment, the multilayer film comprises:
(i) a first layer having an index of refraction from about 2.0 to about
2.55 and comprising a first metal oxide material;
(ii) a second layer having an index of refraction from about 1.38 to about
1.5 and comprising a second metal oxide;
(iii) a third layer having an index of refraction from about 2.0 to about
2.55 and comprising the first metal oxide material; and
(iv) a fourth layer having an index of refraction from about 1.38 to about
1.5 comprising the second metal oxide, wherein the indices of refraction
are measured at a reference wavelength of 550 nanometers.
In a preferred embodiment, the third layer is electrically conductive. In
yet another preferred embodiment, the first and third layers comprise high
refractive index materials selected from the group consisting of titanium
oxides niobium oxides, and tantalum oxides and the second and fourth
layers comprise silicon dioxide. For substrates that comprise ophthalmic
lens, the lens surface preferably has an electric potential that is less
than about 100 volts.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-sectional view of an ophthalmic lens produced in
accordance with this invention.
FIG. 2 is a schematic diagram of an ion assisted deposition apparatus
employed to produce the anti-reflection coating.
FIG. 3 is a graph of electrostatic potential vs. layers in a coating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is based in part on the discovery that increasing the
electrical conductivity in one or more layers of a multilayer
anti-reflection coating confers the coating with anti-static
characteristics. Indeed, even when subjected to frictional forces, the
inventive anti-reflection coating does not develop any appreciable amount
of electrostatic charge.
The inventive anti-reflection coating demonstrates improved resistance to
dirt and stains as well, thereby obviating the need for employing a
hydrophobic outer layer over the anti-reflection coating. The presence of
this hydrophobic outer layer can adversely effect the optical
characteristics of the ophthalmic lenses including, for instance, color
consistency and reflectivity, and increase their production costs.
However, prior to describing the invention is further detail, the following
terms will be defined:
The term "substrate" refers to a material which preferably has superior
structural and optical properties. Crystalline quartz, fused silica,
soda-lime silicate glass, and plastics such as from polymers based on
allyl diglycol carbonate monomers (available as CR-39.TM. from PPG
Industries, Inc., Hartford, Conn.) and polycarbonates such as Lexan.TM.,
available from General Electric Co., are preferred substrate materials.
Substrates include ophthalmic lenses (including sunglasses). Preferred
ophthalmic lenses also include laminated lenses that are fabricated by
bonding two lens wafers (i.e., a front wafer and a back wafer) together
with a transparent adhesive. Laminated lens wafers are described, for
example, in U.S. Pat. Nos. 5,149,181, 4,857,553, and 4,645,317 and U.K.
Patent Application, GB 2,260,937A, all of which are incorporated herein.
Commercially available plastic ophthalmic lenses that are coated with a
polymeric scratch resistance coating that may be about 1 .mu.m to about 12
.mu.m thick are also suitable substrates. The thickness of the polymeric
scratch resistance coating will depend, in part, on the substrate
material. Generally, plastic materials such as polycarbonates will require
thicker coatings. Suitable substrates further include glass ophthalmic
lenses, as described, for instance, in U.S. Pat. Nos. 3,899,315 and
3,899,314, both of which are incorporated herein. As used herein the term
"lens" refers to both single integral body and laminated types.
The term "anti-reflection coating" or "AR coating" refers to a
substantially transparent multilayer film that is applied to optical
systems (e.g., surfaces thereof) to substantially eliminate reflection
over a relatively wide portion of the visible spectrum, and thereby
increase the transmission of light and reduce surface reflectance. Known
anti-reflection coatings include multilayer films comprising alternating
high and low refractive index materials (e.g., metal oxides) as described,
for instance, in U.S. Pat. Nos. 3,432,225, 3,565,509, 4,022,947, and
5,332,618, all of which are incorporated herein. However, unlike prior art
AR coatings, the inventive AR coatings employ one or more electrically
conductive high and/or electrically conductive low refractive index
layers. The thickness of the AR coating will depend on the thickness of
each individual layer in the multilayer film and the total number of
layers in the multilayer film. The inventive AR coating can include any
number of layers. Preferably, the AR coating for the ophthalmic lens has
about 3 to about 12 layers, more preferably about 4 to about 7 layers, and
most preferably about 4 layers. Preferably, the AR coating is about 100 to
about 750 nm thick. For use with ophthalmic lenses, the AR coating is
preferably about 220 to about 500 nm thick.
The term "adhesion layer" refers to a film or coating that is formed on the
transparent substrate prior to depositing the multilayer film of the
anti-reflection coating. The adhesion layer promotes bonding of the
anti-reflection coating to the substrate. Any suitable transparent
material can be used to form the adhesion layer including chromium oxide.
Use of an adhesion layer is optional and the choice of material employed
will depend, in part, on the substrate material and the material
comprising the first layer of the multilayer anti-reflection coating. The
thickness of the adhesion layer is not critical although it is preferably
kept to a thickness just sufficient to effectively bond the substrate to
the anti-reflection coating but not to have a significant optical effect.
If the chromium is not oxidized sufficiently or if the adhesion layer is
too thick, then this layer will cause absorption of light and reduce
transmission through the AR coating. The adhesion layer may be
electrically conductive which may further enhance the anti-static
characteristics of the multilayer anti-reflection coating.
The term "high refractive index material" refers to materials having an
index of refraction (at a referenced wavelength of about 550 nm) that is
preferably greater than about 2.0, more preferably from about 2.1 to about
2.55, and most preferably from about 2.2 to about 2.4.
The term "low refractive index material" refers to materials having an
index of refraction (at a referenced wavelength of about 550 nm) that is
preferably less than about 1.5, more preferably from about 1.38 to about
1.5, and most preferably from about 1.45 to about 1.46.
The term "anti-static" refers to the ability of a material not to retain or
develop an appreciable amount of electrostatic charge. With respect to an
ophthalmic lens coated with the anti-reflection coating of the present
invention, the lens surface preferably remains substantially
electrostatically neutral wherein the coated lens surface has an electric
potential that is less than about 100 volts, more preferably less than
about 75 volts, and most preferably less than about 50 volts, when
measured in the neutral state or discharged state. By "neutral state" or
"discharged state" is meant that the lens surface has not been subject to
friction or other electrostatic charge generating processes or devices
within about 5 seconds prior to measurement. Conversely, the "charged
state" refers to the condition of a lens immediately, and up to about 5
seconds, after being subject to friction or other electrostatic charge
generating processes or devices.
Preferably, for an ophthalmic lens coated with the anti-reflection coating,
the coated lens surface has an electric potential that is less than about
600 volts, and preferably about 0 to about 500 volts, and most preferably
about 0 to about 300 volts or less when measured immediately after being
rubbed with a cloth made of a synthetic (e.g., polyester) or natural
(e.g., cotton) material. Further, for an ophthalmic lens coated with the
anti-reflection coating, preferably, the coated lens surface has an
electric potential that is less than about 100 volts, more preferably
about 0 to about 75 volts or less, and most preferably about 0 to about 50
volts or less within about 5 seconds after being rubbed. As is apparent,
one of the features of the inventive AR coating is its ability to
discharge or dissipate electric charge and prevent charge buildup.
For purposes of this invention, volts shall include the magnitudes of both
positive and negative voltages so that a lens surface having an electric
potential of 100 volts or less, covers the range from -100 to +100 volts.
A preferred method of fabricating a conductive AR coating is to employ
electrically conductive high and low refractive index materials that
comprise metal oxides. Metal oxides with high refractive indices include,
for example, oxides of titanium, cerium, bismuth, zinc, iron, niobium,
tantalum, zirconium, chromium, tin, indium, and mixtures thereof.
Particularly preferred electrically conductive high refractive index
materials are niobium oxides and titanium oxides derived by reactive
sputtering or evaporation. Metal oxides with low refractive indices
include, for example, oxides of silicon; suitable low refractive index
materials also include aluminum oxyfluoride and magnesium oxyfluoride.
Alternatively, one or more of the metal oxide materials can be replaced
with non-oxide materials having the requisite refractive index. For
instance, zinc sulfide can be used in electrically conductive high
refractive index material and magnesium fluoride and thorium fluoride can
be employed in electrically conductive low refractive index materials.
These non-oxides are described in U.S. Pat. No. 5,332,618.
The multilayer film, which forms the inventive AR coating, comprises at
least one layer that is electrically conductive. It is believed that the
presence of the one or more electrically conductive layer effectively
prevents appreciable electrostatic charge buildup by continuously
discharging the same. The result is an AR coating which is anti-static.
The terms "electrically conductive high refractive index material" and
"electrically conductive low refractive index material" refer to a high
and low refractive index materials that are suitable for use in conductive
anti-reflection coatings. Preferably, an electrically conductive high
refractive index material comprises a metal oxide having a high refractive
index. Conversely, an electrically conductive low refractive index
material comprises a metal oxide having a low refractive index.
A preferred method of fabricating such materials is to synthesize a metal
oxide in an environment so that the metal oxide film produced is
non-stoichiometric or sub-oxidized. The resulting metal oxide film has the
electrical properties described above.
As further described herein, in non-stoichiometric metal oxides the ratio
of oxygen to metal is less than the theoretical stoichiometric ratio for
any particular structure. (Metal oxides wherein the ratio of metal to
oxygen is stoichiometric are generally referred to as dielectric materials
that are non-electrically conductive.) However, the electrically
conductive materials can also comprise a mixture of (1) stoichiometric
metal oxides and (2) stoichiometric oxides and/or non-reacted metal atoms.
Methods of synthesizing non-stoichiometric metal oxides include reactive
sputtering and evaporating of metal in oxygen deficient environments.
It is known that stoichiometric titanium dioxide (i.e., TiO.sub.2) has a
specific conductivity of less than 10.sup.-10 S/cm whereas TiO.sub.1.9995
yields a value of 10.sup.-1 S/cm. Thus it is expected that suitable
electrically conductive high refractive index materials can be fabricated
by reacting titanium with a non-stoichiometric amount of oxygen such that
the titanium oxide produced has the nominal formula TiO.sub.x wherein x is
less than 2, preferably about 1.3 to about 1.9995, more preferably about
1.5 to about 1.9995, and most preferably about 1.7 to about 1.9995.
It is believed that TiO.sub.2 is the predominant form of titanium oxide
formed. However, it is believed that other forms are produced as well.
Thus, unless otherwise stated, TiO.sub.x will represent all forms of
titanium oxide produced. It should be noted that when employing titanium
oxides as the layer of electrically conductive high refractive index
material, the particular structure of the titanium oxides produced is not
critical so long as the layer has the desired optical characteristics
(e.g., refractive index and transparency) necessary for the
anti-reflection coating, and the coated ophthalmic lens has the
anti-static properties defined above.
When the inventive AR coating is a multilayer film comprising a layer of
electrically conductive low refractive index material, it is expected that
suitable electrically conductive low refractive index materials can be
fabricated by reacting silicon with a non-stoichiometric amount of oxygen
such that the silicon oxide has the nominal formula SiO.sub.x wherein x is
less than 2, preferably about 1.5 to about 1.99, more preferably about 1.7
to about 1.99 and most preferably 1.8 to about 1.99.
Similarly, it is believed that SiO.sub.2 is the predominant form of silicon
oxide formed. However, it is believed that other forms are produced as
well. Thus, unless otherwise stated, SiO.sub.x will represent all forms of
silicon oxides produced. Likewise, when employing silicon oxides as the
layer of electrically conductive low refractive index material, the
particular structure of the silicon oxides produced is not critical so
long as the layer has the desired optical characteristics necessary for
the anti-reflection coating and the coated ophthalmic lens has the
anti-static properties.
Thus, in general, when employing metal oxide materials to construct either
a layer of low or high refractive index material, the particular formula
or structure of the metal oxide is not critical so long as the layer has
the desired optical properties. In the case of forming a layer of
electrically conductive low or high refractive index material, the other
criterion is that the anti-reflection coating has the anti-static
properties.
Since only one or more layers of the multilayer film of the inventive AR
coating needs to be electrically conductive, it is understood that. except
in the case where all the layers are electrically conductive, the other
non-electrically conductive layer(s) of the film can comprise conventional
dielectric materials such as titanium dioxide for the high refractive
index layer and silicon dioxide for the low refractive index layer. It is
further understood that the term "metal oxide" or "metal oxides" generally
refers to both electrically conductive and nonconductive metal oxides.
Thus, for instance, titanium oxides comprise electrical conductive
TiO.sub.x as defined above as well as titanium dioxide (i.e., TiO.sub.2) a
dielectric. Similarly, silicon oxides comprise electrical conductive
SiO.sub.x as defined above as well as silicon dioxide (i.e., SiO.sub.2) a
dielectric.
In designing and fabricating the multilayer film of an anti-reflection
coating, selection of the material(s) for the electrically conductive
layer should take into account the electrical conductivities of the
various metals available to form suitable metal oxides. Preferably, the
electrically conductive high or low refractive materials should be formed
from metals having the higher electrical conductivity.
A further method of fabricating electrically conductive materials is to
first produce the metal oxide dielectric films and thereafter introduce
dopants into the film. The dopant is selected from conductive materials
that can be the same material as the metal. This technique is particularly
suited if a non-oxide (e.g., MgF.sub.2) is employed. The dopant can be
introduced by any suitable means including diffusion and ion implantation.
See, for example, Wolf & Tauber, "Silicon Processing for the VLSI Era,"
Vol. 1, pp. 242-332 (1986) which is incorporated herein by reference.
Methodology
The substantially transparent multilayer film structure of the inventive AR
coating can be fabricated by conventional film deposition techniques
(chemical and physical) including reactive sputter deposition, chemical
vapor deposition and electron beam evaporation, with and without ion
assist. These techniques are described in "Thin Film Processes" and "Thin
Film Processes II," Vossen & Kern, editors (1978 and 1991) Academic Press,
which are incorporated herein by reference. The method most suited will
depend on, among other things, the substrate (material and size) and the
particular conductive metal oxides employed.
Sputtering techniques involve the physical ejection of material from a
target as a result of ion bombardment. The ions are usually created by
collisions between gas atoms and electrons in a glow discharge. The ions
are accelerated into the target cathode by an electric field. A substrate
is placed in a suitable location so that it intercepts a portion of the
ejected atoms. Thus, a coating is deposited on the surface of the
substrate. In reactive sputtering, a reactant gas forms a compound with
the material which is sputtered from the target. When the target is
silicon and the reactive gas is oxygen, for instance, silicon oxides,
usually in the form of SiO.sub.2 is formed on the surface of the
substrate. Another sputtering technique is to first form a sputtered metal
layer on a substrate and thereafter expose this layer to a reactive gas
(e.g., oxygen) to form a metal oxide. Sputtering devices are described for
instance in U.S. Pat. Nos. 5,047,131, 4,851,095 and 4,166,018, all of
which are incorporated herein.
Chemical vapor deposition is the formation of a non-volatile solid film on
a substrate by the reaction of vapor phase chemicals (reactants) that
contain the required constituents. The reactant gases are introduced into
a reaction chamber and are decomposed and reacted by a heated surface to
form the thin film.
The conditions required to effect such depositions are well known in the
art. For example, chemical vapor deposition, including low-pressure
chemical vapor deposition (LPCVD), plasma enhanced chemical vapor
deposition (PECVD), photon-induced chemical vapor deposition (PHCVD), and
the like, is described by Wolf & Tauber, "Silicon Processing for the VLSI
Era," Vol. 1, pp. 161-197 (1986) which is incorporated herein by
reference.
Other suitable film deposition techniques include electron beam evaporation
and ion-assisted deposition. In electron beam evaporation, an evaporation
source (i.e., electron beam) is employed to vaporize the desired target
material. The evaporated atoms condense on a substrate situated within the
vacuum chamber. See, "Thin Film Processes II" at pages 79-132. In
ion-assisted deposition, low-energy ion bombardment of the substrate
surface during deposition of evaporated atoms provides surface cleaning,
improved nucleation and growth, and in situ annealing which produces
evaporated coatings of improved quality. For a discussion of ion-assisted
deposition, see Stelmack, et. al., "Review of Ion-Assisted Deposition:
Research to Production" Nuclear Instruments and Methods in Physics
Research B37/38 (1989) 787-793, which is incorporated herein.
A preferred embodiment of the invention is illustrated in FIG. 1 which
comprises an ophthalmic lens 10 that has a conductive anti-reflection
coating disposed on a surface. The coating comprises four transparent,
substantially colorless layers 11-14 which are formed of at least two
different materials, in which one is a high refractive index material and
the other is a low refractive index material. Layers 11-14 comprise an
anti-reflection coating which is also referred to as an "AR stack" or
"stack." Preferably, prior to forming the AR stack, an adhesion layer 10A
comprising chromium oxides is deposited on the substrate surface.
Preferably, the AR stack or coating comprises alternating high and low
refractive index materials such that each layer has a refractive index
different from that of any adjoining layer. Preferably, the index of
refraction of each low refractive index material is less than about 1.5 at
a wavelength of about 550 nm, which is a preferred designed wavelength for
visible light transmission; the index of refraction of each high
refractive index material is greater than about 2.0 at a wavelength of
about 550 nm; and, each layer comprises a electrically conductive metal
oxide. The first layer of the AR stack, which is formed on the substrate
(or on the adhesion promotion layer, which is optional) normally comprises
a high index material.
In the embodiment as shown in FIG. 1, layers 11 and 13 comprise high
refractive index materials, wherein layer 11 has a thickness of about 7 nm
to about 15 nm, more preferably from about 9 nm to about 13 nm and most
preferably from about 10 nm to about 12 nm and wherein layer 13 has a
thickness of about 90 nm to about 130 nm, more preferably from about 100
nm to about 120 nm and most preferably from about 105 nm to about 115 nm.
Layer 11 is designated the first layer of this 4 layer stack. Conversely,
layers 12 and 14 comprise a low refractive index material wherein layer 12
has a thickness of about 15 nm to about 40 nm, more preferably from about
20 nm to about 35 nm, and most preferably from about 23 nm to about 31 nm,
and wherein layer 14 has a thickness of about 55 nm to about 105 nm, more
preferably from about 65 nm to about 95 nm, and most preferably from about
75 nm to about 85 nm.
The multilayer film forming the AR coating can comprise any suitable number
of layers of high/low refractive index materials. For most optical
applications, it is desirable that the AR coatings reduce the surface
reflectance to an extremely low value over an extended spectral region so
as to maintain the proper color balance. The number of layers will depend
on, among other things, the substrate material, the particular
anti-reflection properties desired and compositions of the high and low
refractive index materials used. Generally, greater anti-reflection can be
achieved by increasing the number of layers of alternating high and low
refractive index layers but there is a concomitant decrease in the
spectral region of anti-reflection. Furthermore, as described, in U.S.
Pat. Nos. 3,432,225 (3-layer design), 3,565,509 (4-layer design), and
5,332,618 (8-layer design), mathematical formulas have been developed to
simulate the optics of multilayer anti-reflection coatings so that their
design can be optimized.
Experimental
The electron beam ion-assisted deposition apparatus employed to produce AR
stacks of the present invention is shown in FIG. 2 and comprises a vacuum
chamber 100 which contains ion gun 102 and electron beam evaporation
source 106 that are positioned at the base of the vacuum chamber. Baffle
108 separates the ion gun from the E-beam source. Located at the upper
portion of the chamber are lens dome 112 and substrate support 110. The
vacuum chamber is available from Balzer Ltd., Balzer, Liechtenstein, as
model Balzer 1200 Box Coater. It is equipped with a Balzer EBS 420
Electron Beam source. The ion gun is a Commonwealth mark II Ion Source
from Commonwealth Scientific Corp., Alexandria, Va.
In operation, a substrate (e.g., ophthalmic lens) is placed on the
substrate support and thereafter a vacuum is created and maintained with
vacuum pump 114. Initially, the ion gun shutter 104 is closed to prevent
ion energy from striking the substrate until the ion gun has stabilized to
the preset energy level. Similarly, shutter 113 covers the E-beam source
until the target is about to evaporate. Argon is employed as the ionizing
gas for the ion gun. Normally, the substrate surface is subject to ion
etch prior to deposition of the chromium oxide adhesive layer. To produce
a metal oxide layer, the E-beam source is activated to produce a metal
evaporant of the requisite concentration. Oxygen from oxygen source 116
reacts with the evaporant to form metal oxide which is deposited on the
substrate surface. Subsequent metal oxide layers are produced in a similar
manner.
AR coatings having the structure as shown of FIG. 1 were fabricated with
the device of FIG. 2. Representative operating parameters in the
fabrication of a preferred AR coating and the characteristics of the
individual layers are set forth in Table 1. The substrates used were
laminated single vision lenses each having a scratch resistant coating.
TABLE 1
__________________________________________________________________________
Thickness
Index @ 550
O.sub.2 Pressure
Deposition
Material (nm) nm QWOT*
(mbar)
rate (nm/sec)
__________________________________________________________________________
Adhes.
Chromium
<1.0 .about.2.50
8 .times. 10.sup.-5
Layer
oxide
Layer 1
Titanium oxide
11.33
2.271 0.1871
2 .times. 10.sup.-4
0.3
(TiO.sub.x)
Layer 2
Silicon dioxide
27.30
1.461 0.2901 0.8
(SiO.sub.2)
Layer 3
Titanium oxide
111.07
2.271 1.8344
2 .times. 10.sup.-4
0.3
(TiO.sub.x)
Layer 4
Silicon dioxide
80.91
1.461 0.8597 0.8
(SiO.sub.2)
__________________________________________________________________________
*Quarter Wave Optical Thickness
Prior to commencing deposition, the lens substrates were ultrasonically
cleaned using deionized water and then degassed at 95.degree. C. for 2
hours. Thereafter, lenses were loaded on the substrate support and the
pressure in the chamber was lowered to about 6.times.10.sup.-6 mbar. The
substrate surface was ion etched for approximately 4 minutes with the ion
gun operating at 0.9 A/110 V. In forming the adhesive layer, chromium
target material was initially covered with shutter 113 as the chromium is
heated by the electron beam from the E-beam evaporation source. The
shutter was removed before the chromium evaporated. During the formation
and deposition of the chromium oxide layer, oxygen was introduced
sufficient to raise and maintain the chamber pressure to 8.times.10.sup.4
mbar. As is apparent, the ion gun shutter was also removed during
deposition. The succeeding 4 layers that comprise the AR coating were
deposited in a similar manner. Preferably, the overall pressure of the
vacuum chamber is maintained at about 2.times.10.sup.-4 mbar or less
throughout the deposition of each of the layers. The second titanium oxide
layer (layer 3) of the AR coating formed was found to be electrically
conductive.
Lenses coated with the inventive AR coating of Table 1 were tested for
anti-static properties. To induce electrostatic charge buildup, the
coatings were rubbed with a lint-free cotton cheesecloth and a 100%
polyester Luminex.RTM. (Toray Industries, Inc., Tokyo, Japan) lens
cleaning cloths. Measurements were conducted in two separate environments:
with and without air conditioning. Air conditioning tends to reduce the
amount of moisture in the air and thereby affect static properties. Three
measurements were made for each lens. Prior to any rubbing, the lenses
were taken out of their packaging and allowed to acclimate to the
environment for at least 30 minutes. The voltages on the front surfaces
were then measured with a TI 300 static meter (Static Control Services,
Inc., Palm Springs, Calif.). Next, each lens was rubbed for ten strokes
(back and forth--four inches each way) on the appropriate cloth, and the
electrostatic measurement was made immediately. The third measurement was
made following a five seconds interval after the lenses were rubbed.
Between each measurement, the lenses were placed in front of an Endstat
2000 Deionizer (Static Control Services, Inc.) to eliminate any residual
static charges.
The measurements, which are set forth in Table 2, demonstrate that lenses
coated with the inventive AR coating developed insignificant or no
electrostatic charge.
TABLE 2
______________________________________
NO RUB RUB RUB + 5 SEC
______________________________________
Without Air
Conditioning
Cotton Cheesecloth
0 -50 0
Polyester Cloth
0 100 0
With Air
Conditioning
Cotton Cheesecloth
0 -100 -25
Polyester Cloth
0 0 0
______________________________________
(Measurements were made in volts)
Laminated single vision lenses each having a scratch resistant coating and
coated with conventional anti-reflection coatings that included a
hydrophobic outer layer were also tested for anti-static properties in the
manner described above. These "stock" lenses were available from various
ophthalmic lens manufacturers. The results are shown in Tables 3 through
6. The degree of hydrophobicity of the outer surface of each AR coating is
proportional to its contact angle which was measured with a Tantec Angle
Meter, available from Tantec Inc., Schaumberg, Ill.
Tables 3 (cotton cheesecloth) and 4 (polyester cloth) comprise measurements
taken in a room without air conditioning. Similarly, Tables 5 (cotton
cheesecloth) and Table 6 (polyester cloth) comprise measurements taken in
one with air conditioning. (Measurements were made in volts). As is
apparent, lens number 1 in each of Tables 3-6 corresponds to the
appropriate inventive lens in Table 2. Lens 2-7 of Table 3 had the same
anti-reflection coatings as lens 2-7 of Table 4, respectively. Similarly,
lens 2-9 of Table 5 had the same anti-reflection coatings as lens 2-9 of
Table 6, respectively.
As is apparent from the comparative dam, the inventive AR coating
demonstrated superior anti-static properties compared to the prior an
anti-reflection coatings available from ophthalmic lens manufacturers.
Furthermore, the inventive AR coating does not require an outer
hydrophobic coating which is present in all of the conventional AR
coatings tested.
TABLE 3
______________________________________
Lenses No Rub Rub Rub + 5 sec
Contact Angle
______________________________________
1 0 -50 0 31.degree.
2 -150 -700 -200 100.degree.
3 0 -950 -300 95.degree.
4 -250 -1000 -500 100.degree.
5 -213 -2375 -1000 95.degree.
6 -350 -3250 -2000 95.degree.
7 -700 -4500 -2000 81.degree.
______________________________________
TABLE 4
______________________________________
Lenses No Rub Rub Rub + 5 sec
Contact Angle
______________________________________
1 0 100 0 31.degree.
2 -150 -950 -325 100.degree.
3 0 -1350 -150 95.degree.
4 -250 -1000 -500 100.degree.
5 -213 -4500 -2750 95.degree.
6 -350 -5500 -4000 95.degree.
7 -700 -3000 -2250 81.degree.
______________________________________
TABLE 5
______________________________________
Lenses No Rub Rub Rub + 5 sec
Contact Angle
______________________________________
1 0 -100 -25 31.degree.
2 -100 -800 -500 100.degree.
3 -150 -1750 -850 100.degree.
4 0 -2000 -700 95.degree.
5 -450 -3500 -2250 81.degree.
6 -163 -4500 -3250 95.degree.
7 -500 -6500 -5000 95.degree.
8 -250 -8500 -6000 100.degree.
9 -1250 -10000 -9500 95.degree.
______________________________________
TABLE 6
______________________________________
Lenses No Rub Rub Rub + 5 sec
Contact Angle
______________________________________
1 0 0 0 31.degree.
2 -100 -2250 -450 95.degree.
3 -150 -1250 -600 100.degree.
4 0 -2750 -650 100.degree.
5 -163 -4500 -2250 81.degree.
6 -500 -5875 -3500 95.degree.
7 -450 -10000 -6000 95.degree.
8 -250 -8000 -5000 100.degree.
9 -1250 -10000 -9500 95.degree.
______________________________________
Layer-by-layer Analysis of AR Coating
To determine what significant effect, if any, the individual layers of the
AR coating had on the anti-static properties of AR coatings, a
layer-by-layer analysis of the AR coating having the five layer structure
described in Table 1 was conducted. In this analysis, five plastic front
wafers were coated, each having a different number of layers. (The wafers
used were plastic and coated with a scratch resistant polymeric layer.)
The first wafer was coated with (1) the chromium oxide adhesion layer
only. The second wafer was coated with (1) the chromium oxide adhesion
layer and (2) first TiO.sub.x, and so on, so that the fifth wafer
comprised the five layer structure.
After formation of the five coated wafers, the voltage on the front
surfaces of each wafer was measured with a TI 300 static meter. Each wafer
was rubbed for ten strokes (back and forth--four inches each way) on a
lint-free cotton cheesecloth and the measurements were made immediately.
In the third test, five seconds lapsed after the lenses were rubbed,
before being measured. As a control, the electrostatic voltages of two
plastic front wafers (i.e., controls 1 and 2) were also measured. Each
control wafer was coated with a different scratch resistant polymeric
coating. The five wafers tested had the same scratch resistant polymer
coating as control 1.
It was found that the electrostatic charge remained high for the first,
second, and third wafers; however, the fourth wafer which comprised: (1)
the chromium oxide adhesive layer, (2) the first TiO.sub.x layer, (3) the
first SiO.sub.2 layer, and (4) the second TiO.sub.x layer, showed a
dramatic reduction is electrostatic charge. Analysis showed that for the
second TiO.sub.x layer, x was about 1.78. Thus, at least with respect to
AR coatings having alternating high and low refractive index materials
comprising titanium oxides and silicon oxides, the second high refractive
index material preferably is TiO.sub.x wherein, x is about 1.3 to about
1.9995, more preferably about 1.5 to about 1.9995, and most preferably
about 1.7 to about 1.9995.
It should be emphasized that while the examples shown herein comprise only
two different high and low index materials (i.e., SiO.sub.x and TiO.sub.x)
in the particular design, similar anti-reflection coating structures could
be designed with two or more high index materials and/or two or more low
index materials, or even a material such as aluminum oxide of some
intermediate refractive index.
Furthermore, in certain cases, it may be advantageous to use mixtures of
materials or complex compounds. A mixture of cerium oxide and zinc oxide
could be used for the high index films and a mixture of silicon dioxide
and magnesium fluoride for the low index films. Other mixtures might be
chosen to suit a particular deposition technique or to take advantage of a
particular optical or physical property of a material.
Ophthalmic lens having the anti-reflection coating preferably has a
transmittance at 550 nm of between about 98.0 to about 99.5%, more
preferably between about 98.5 to about 99.5%, and most preferably between
about 99.0 to about 99.5%. Moreover, the ophthalmic lens has a reflectance
at 550 nm of between about 0.5 to about 2.0%, more preferably between
about 0.5 to about 1.5%, and most preferably between about 0.5 to about
1.0%.
Although only preferred embodiments of the invention are specifically
disclosed and described above, it will be appreciated that many
modifications and variations of the present invention are possible in
light of the above teachings and within the purview of the appended claims
without departing from the spirit and intended scope of the invention.
Top